how turbo diesel works ?

from the start i admit i don't know a lot about diesel engines, only the basic principle about how they work.
everywhere and i mean EVERYWHERE i read that the most important advice everybody gives you is that you should never drive a diesel under 2000 rpm, or push the throttle hard when you are under this engine speed, because disasters WILL happen: the turbine will fall from the engine, or it will explode, or the planets will realign etc.

but nobody is able to explain me WHY that is. everybody seems to know it, but nobody knows the reason. it's just common knowledge.

well i'm not satisfied with that, so i need to know: is there any technical reason not to floor your turbo diesel under 2000 rpm ? other than the fact that it's useless. of course

I see no reason why (unless the engine is stone cold, but that is for any engine). If it was harmfull, it was inhibited in the engine's calibration.
VW's 1.9 TDI runs very well below 2000 rpm, which usually is my shift point in that car (my gf has a VW Touran), good acceleration with good economy.